However, failure of phase III clinical trial (ECHO-301/KN-252) where Epacadostat an IDO inhibitor in combination with anti-PD-1 antibody pembrolizumab was used in metastatic melanoma patients did not demonstrate improved progression-free survival and OS and thus terminated early (268, 269) have pushed for a re-think on the clinical benefits of IDO inhibitors in cancer. Here, IDO1 is linked to cancer.